No specific person made up the lie. If anyone is to blame, it's Rhaegar and/or Lyanna. They ran away, even though he was married and she betrothed, and from what we know they told no one but the Kingsguards.
This is a deeply irresponsible behaviour and let to a massive catastrophe in the form of a civil war and the deaths of not only themselves, but also their family members and thousands upon thousands of soldiers, civilians, knights and lords. Rhaegars idiocy is unbelievable. How is it possible that a man loved by everyone (except Robert) causes all this and then doesn't even try to stop it by telling the truth?
And Lyanna. I almost can't believe she chose lust and love before her family. Her fiancé? Sure - she didn't chose him, but still we have no indication that she hated him ("Love is sweet, dear Ned, but it cannot change a man's nature" is all we've read her say about Robert, and that does not seem hateful). Although she must have heard of her father's and brother's deaths, and that her other brother and fiancé were marching to war, and that her lover and husband was going to do his best to kill Robert and route Ned's army, and even if he didn't intend on killing him ...marching on someone with 35 000 men means there's a high probability that he dies.
Lyanna Stark chose lust and love above her own family's lives. Is that what is meant by "willful"? She also knew that Robert loved her, and that he had no reason to suspect she ran off willingly. Likely Robert wouldn't have believed the raven scroll saying she loved Rhaegar and was going to marry him, but isn't one failed raven worth the shot at stopping a massive war where her family tries to kill his family and vice versa?
Also ... Rickard tried to marry Lyanna off for southron ambitions. The lord of Storm's End and the liege lord of all the Stormlands is a dear, dear price ... but he would have been even happier having his grandkid sit the Iron Throne. Surely both he and Brandon would accept it - Ned definitely would.
There's still the problem with Aerys though, and since the war wasn't based on a lie but on murder and conspiracy to commit murder, it's likely it would have happened anyway - the rebels simply had no choice. But Lyanna did, and there is not a single evidence suggesting she tried to stop the disastrous upcoming events.
I'm not bashing Rhaegar as much because I have no hope in him being a good man. Lyanna's actions bothers me though.

In the last episode of season 7, Bran the Almighty said "Robert's Rebellion was based on a lie", but I do not think this is true.
Yes: Lyanna was not abducted, and she followed Rhaegar willingly.
But since the rebellion didn't start because of this, but because King Aerys burned Rickard and strangled Brandon to death, and asked for the heads of Robert and Ned, it was not based on a lie. Jon Arryn did NOT raise his banners because the fiancée of his ward was "abducted", and no declaration of war was done on Rickard's/Brandon's parts either. The shit hit the fan when the Mad King decided he could kill whomever he wanted to.
One could argue that it started before that - that it started with Lyanna/Rhaegar running off, but in that case it started long before that, as Rhaegar crowned Lyanna QoLaB a year past. And before that, the Mad King's wife gave birth to Rhaegar. THAT has to be the start. Oh, no, wait ... she also had parents, et cetera. Something important always comes after something else (unless Planetos' universe had a Big Bang as well, but you get what I mean).
The rebellion started because the Mad King was batshit insane and murdered people left and right (like the two hundred northmen with Rickard), and wanted to continue this. This is not a lie, and therefore Robert's Rebellion was NOT based on a lie.
What do you think?

Oh my god. Perhaps because she should understand thousands upon thousands will die if she does not? Her family did almost go extinct because of her! Isn't that more important than a pair of beautiful eyes? A pair of beautiful eyes that now are dead because of her and the stupid bearer of those eyes.

In this episode Jon asked Tyrion how many people lived there (King's Landing), and Tyrion answered "one million". Then Jon said that that's more than the entire North's population.
First of all: before it was 500 000, according to Jaime. Has the population grown so much in 17 years?
Secondly: how is this possible? I know it's sparsely populated, but it's still huge. Shouldn't it be much more?
best regards

Perhaps it's brought up before, but I haven't seen anthing about it. I noticed today, that not only Gregor, but all the kingsguards, have new armor. It's not silver/gold anymore, but rather black/dark grey/silver. Has this been the case since the last episode of season 6
Why?

What in the world is up with him? What's the point of his character in the series? He was brilliant when he destroyed Dany's fleet, but now he's suddenly a total coward. Just a complete waste of space and time in the series.
I just don't get it?

No, that would be such a stereotypical, boring clichée. She has to die. She has been the favorite winner all the way since season 1.
It would be a huge dissapointment if she survives and rules happliy ever after. This is not "bittersweet" in any way - it is plainly sweet.
GRRM said that the one who sits the Iron Throne at the end would be "someone unexpected", meaning "not Danaerys". In GRRM's mind, Jon is unexpected, even if he isn't in our's.
I wouldn't be suprised if they changed the end from the book-ending to something they created themselves, but then it would be a change for the worse ... as basically all major changes have been.

Hmm. I guess the question is if Robert would believe that Tyrion indeed was guilty. If not, the story wouldn't be changed very much except for the Tullys being exterminated. If he did believe it, the story might have gone the opposite way, with Robert takin up arms against his wife's family. Facing eachother head-on, Tywin wouldn't have much of a chance, really. It would be, essentially, the Westerlands against the rest of Westeros (except perhaps Dorne ... who, however, might have joined if they were promised justice for Elia and her children). The Ironborn would remain neutral or join Robert, depending on how bitter Balon is at the moment
Unless, of course ... Cersei manages to kill Robert before all this, but I doubt that would be the case if the king was alive and wanted to defeat the Lannisters.